Lead and lead alloys



Patented Nov. 2, 1937 LEAD AND LEAD ALLOYS William Thomas Butcher, Ilford, England, as-' UNITED STATES PATENT OFFICE rial No. 115,629. In 12, 1935 This invention relates to the treatment of tincontaining lead alloys, and more particularly impure lead containing one or more additional metals, suchfor example as antimony, arsenic, copper and tellurium.

One method commonly used in the separation of tin from such alloys is a furnace or drossing process in which the impure met-a1 is heated to 800-'900 C. in the presence of air when the impurities form oxide slags or drosses on the top of the molten metal in the following order: tin, arsenic and antimony. It is found that the tin slags or drosses so obtained always contain some oxides of the associated metals, e. g. lead, antimony, arsenic or copper, and that tin is not directly recoverable from such slag or dross in form pure enough for commercial purposes. The above process has the disadvantages'of being slow since the oxidation only takes place at the surface of the metal, involving considerable loss of heat, while on account of the amounts of lead remaining in the oxide slags or drosses the yield of refined metal is decreased, and in addition the oxide slags or drosses have a low commercial value.

The present invention provides a process of treating tin-containing lead alloys, in which tin, removed from the molten alloy in the form of oxide by the action, in the presence of a lead halide, of a reducible compound of a. metal, is replaced by a metal other than lead obtained on such reduction. As examples of such reducible compounds oxides of antimony, arsenic and copper may be mentioned. The tin oxide formed by the oxidation of the tin present in the alloy is taken up by the lead halide, which separates in a layer on toy of the alloy, and is easily removable. The metal formed bythe reduction of the reducible metallic compound by the tin enters the metal of the bath and becomes alloyed therewith. By carrying out the oxidation in the presence of a lead halide it is found that the tin can be oxidized preferentially, and that the tin oxide removed with the lead halide can be obtained substantially uncontaminated with oxide of lead, or with oxides of other metals such as antimony, arsenic or copper which may be present in the alloy. Fur--. thermore, this process has the advantage that it can be carried out at a much lower temperature than the older furnace process described Great Britain September 14 Claims. (01. 75-166) above, so the operation can be conducted in simple and inexpensive apparatus instead of a reverberatory furnace, which results in considerable saving in cost, upkeep of plant, fuel and labour, and in addition the invention enables the tin to be recovered in a purer condition than is possible lead to be readily alloyed with metals, such as antimony, arsenic or copper which may not ordinarily be easy to introduce into lead.

A suitable lead halide flux for separating the tin oxide from the lead alloyis lead chloride, but the other halides of lead can also be employed for this purpose, and lead fluoride has been found to be suitable. Mixtures of lead halides can also be employed. One method of utilizingv ,lead chloride resides in the formation thereof in situ in the bath by blowing chlorine into the molten metal or by adding lead oxychloride to the bath.

The layer of lead halide which separates on top of the bath contains the tin oxide, and-after removal of this layer from the molten metal the lead halide may be separated from the tin oxide as described later. Effective contact between the metal and lead halide and the selected oxidizing in the older process. The process also enables agent can be obtained by the usual methods ofv stirring or pumping. 1

In the operation ofthe present invention it has been found that the action of the reducible compound in the presence of lead halide is selective in its operation, in that the formation of tin oxide takes place even when other metals are present in the alloy} For example, if antimony,

arsenic, copper or tellurium are constituents of the lead alloy under treatment these substances remain in the metal, whilst the tin is recovered substantiallyuncontaminated with these other metals and in a condition of sumcient purity to allow of its subsequent use in the production of brought about. By this means the economical production of a lead-antimony alloy using antimony oxide ore at the low temperature is effected. In addition it has been found that oxide of arsenic either by itself or in combination with another oxide or oxides, such for example as lead or antimony oxide, remove tin, the resulting arsenic alloying with the metal bath as before. In the 5 molten metal yielding a lead-antimony alloy.

Residues from electrical storage batteries can be used in like manner. Again lead arsenate slags can be employed, in which case the lead alloy is enriched in arsenic. It has further been found that drosses from type metal melting containing tin, antimony and lead in both oxidized and metallic form can be used in this process, the tin being oxidized and retained in the lead chloride layer while the lead and antimony are absorbed by the metallic bath. If insuflicient oxides are present in the raw material these can be supplied by the addition of lead oxide or other suitable oxidizing agents such as sodium nitrate or by'blowing air into the bath. Copper oxide is a suitable oxidizing agent, either by itself or in combination with another oxide or oxides, such for example as lead oxide or antimony oxide.

The process according to the invention is preferably carried out in a mechanically stirred and spouted cast iron melting pot. The pot is provided with a cover to which a ventilating pipe is attached for the removal of anyfume. stirrer is driven at speed sufficient to create a vortex in the metal and to effect contact between the molten alloy and the fluid lead halide layer and the added oxide. The alloy and the lead halide. are heated so as to render them fluid and the oxide material is fed into this vortexthrough a small charging hopper fixed to the cover. The fluid flux formed by the lead halide and oxide material is drawn down through the metal, in such manner as to give good contact between the-metal and the flux, thus bringing about rapid interaction between the tin and the oxides employed in the flux. Stirring is continued until interaction is complete, when the pasty flux is removed for the recovery of tin, and the purified metal is cast out in the usual way.

The following example illustrates how the invention may be carried into practice:-,

42.4 tons of lead alloy of the following composition were taken:

Percent Antimony 10.61 Tin 2.20 'Copper 0.44 Arsenic 1.09

and the temperature brought to just over 500 C.

be 1.17%, and that of the flux 23.07%.

28-cwts. of lead chloride fume produced by volatilization of lead chloride/tin oxide flux in a furnace for recovery of tin oxide were added. The oxidizing agent used was a lead antimoniate slag such as is produced in the softening of crude lead. 23-cwts. of this were added, and after stirring for a short while the flux began to thicken slightly, whereupon it was removed from the.

metal. The tin content of metal was found to removal of the flux, further additions of 23- The- After 2,097,560 cwts. lead chloride fume and 20-cwts. lead anti moniate slag were made and stirring recommenced and continued until, on analysis of the The average analysis of the lead chloride/tin oxide flux showedz- Percent Tin 23 Antimony 0. 3

It will be observed, therefore, that not only was .tin extracted from a.tin-containing lead alloy,

but the simultaneous and expeditious production of a lead alloy of increased antimony content was effected.

The recovery of tin from the flux may be carried out by any suitable method, of which the two following methods are typical examplesz- (a) A lead chloride/tin oxide flux is powdered and treated with hot water, so that the lead chloride is dissolved leaving the tin oxide residue practically free from lead chloride. The hot solution of lead chloride is allowed to cool, when the lead chloride is precipitated and may be recovered by filtration in the usual way. By this means substantially the whole of the lead chloride is recovered and may be used over again'f or the extraction of further tin from lead alloys in the manner described above. The tin oxide residue can readily be reduced to metal by ordinary smelting methods. k

(b) A lead chloride/tin oxide flux is heated to a temperature above 600 C. with free access of air in a suitable furnace, e. g. a reverberatory furnace fired by means of oil or coke, or mixtures of coal and coke, and yields chloride of. lead in the form of a thick fume, and the volatilization can be carried on' until substantially the whole v of the lead chloride has been removed from the mixture. The free access of air or oxygen is important to promotethe volatilization. Secondary air is admitted to the furnace and volatilization of the lead chloride is further promoted by rabbling of the mass. Alternatively a rotary furnace may be used, in which case rabbling of the mass will be unnecessary. The tin oxide is left as a residue. collected in any suitable condensation or dust collection units, and may be used over again for the extraction of further tin from lead alloys in the manner described above. This lead chlo- The lead chloride fume may be ride fumecontains a substantial proportion of lead oxychloride.

What I claim as my invention and desire to secure by Letters Patent is: 1. A process of alloying metals with lead, which comprisesv the steps of treating a molten tinand removing the tin oxide so formed by separating the flux from the alloy 1 2. A process of alloying metals with lead, which comprises thesteps of treating a'molten tin-containing lead alloy with a flux, consisting of a mixture of lead chloride and a reducible compound of a metal selected from the group con-' comprises the steps of treating a molten tin-containing lead alloy with a fiux, consisting of a mixture of a lead halide and an oxide of a metal selected from the group consisting of arsenic, antimony, and copper, thereby effecting oxidation of the tin and replacement thereof in the alloy by the said metal, and removing the tin oxide so formed by separating the flux from the alloy.

4. A process of alloying antimony with lead, which comprises the steps of treating a molten tin-containing lead alloy with a flux, consisting of a mixture of a lead halide and oxide of antimony, thereby efiecting oxidation of the tin and replacement thereof in the alloy by antimony, and removing the tin oxide so formed by separating the flux from the alloy.

5. A process of alloying arsenic with lead, which comprises the steps of treating a molten tin-containing lead alloy with a flux consisting of a mixture of a lead halide and oxide of arsenic, thereby efi'ecting oxidation of the tin and replacement thereof in thealloy by arsenic, and removing the tin oxide so formed by separating the flux from the alloy.

6. A process of alloying copperwith lead, which comprises the steps of treating a molten'tin-containing lead alloy with a flux consisting of a mixture of a lead halide and oxide of copper, thereby effecting oxidation of the tin and replacement thereof in the alloy by copper, and removing the tin oxide so .formed by separating the flux from the alloy.

'7. A process of alloying metals with lead, which comprises the steps of treating, at a temperature of about 500 C, a molten tin-containing lead alloy with a flux, consisting of a mixture of a lead halide and a reducible compound of a metal selected from the group consisting of arsenic, antimony, and copper, said compound being an oxide of said metal or a compound adapted to form an oxide of said metal in situ, thereby effecting oxidation-of the tin and replacement thereof in the alloy by the said metal, and removing the tin oxide so formed by separating the flux from the alloy.

8. A process of alloying antimony with lead, which comprises the steps of treating a molten tin-containing lead alloy with a flux, consisting of a mixture of lead chloride and oxide of antimony, thereby eifecting oxidation of the tin and :tin-containing lead alloy with a flux,

replacement thereof in the alloy by antimo and removing the tin oxide so formed by Separating the flux from the alloy.

9. A process of alloying arsenic with lead, which comprises the steps of treating a molten tin-containing lead alloy with a flux, consisting of a mix ture of lead chloride and oxide of arsenic; thereby eflecting oxidation of the tin and replacement thereof in the alloy by arsenic, and removing the tin oxide so formed by separating the flux from the alloy.

10. A process of alloying copper with lead, which comprises the steps of treating a molten tin-containing lead alloy with a flux, of a mlxtureof lead chloride and oxide of copper,

thereby effecting oxidation of the tin and replace- .ment thereof in the alloy by copper, and removing the tin oxide so formed by separating the flux from the alloy.

11. A process of alloying antimony with lead, which comprises the steps of treating a molten tin-containing lead alloy with a flux, consisting of a mixture of a lead halide and lead antimoniate, thereby efl'ecting oxidation of the tin and replacement thereof in the alloy by antimony, and reconsisting moving the tin oxide so formed by separating the flux from the alloy.

12. A process of alloying arsenic with lead, which comprises the steps of treating a molten consisting of a mixture of a lead halide and lead arseniate, thereby eifecting oxidation of the tin and replacement-thereof in the alloy by arsenic, and removing the tin oxide so formed by separating the flux from the alloy.

13. A process of alloying metals with lead, which comprises the steps ofvforming lead chloride-in situ in a bath of a molten tin-containing lead alloy, treating the alloy with a reducible compound of a metal selected from the group consisting of arsenic, antimony, and copper, said compound being an oxide of said metal or a compound adapted to form an oxide of said metal in situ, thereby effecting oxidation of the tin and replacement thereof in the alloyby the said metal,

and separating the tin oxide so formed from the I alloy.

14. A process-of alloying metals with lead, which comprises the steps of treating a molten tin-containing lead alloy with a flux, consisting of a mixture of lead fluoride and of a reducible compound of a metal selected from the group consisting of arsenic, antimony, and copper, said compound being an oxide of said metal or a compound adapted to form an oxide of said metal in situ, thereby eifecting oxidation of the tin and replacement thereof in the alloy by the said metal, and removing the tin oxide so formed by separating the flux from the alloy.

I WILLIAM THOMAS BUTCHER. 

